CD43 (also named as sialophorin or leukosialin), a heavily sialylated molecule expresses at high levels on most human leukocytes including all T cells and platelets with a molecular weight ranging from 115,000 to 135,000. CD43 expression is defective on the T cells of males with the Wiskott-Aldrich syndrome, an X chromosome-linked recessive immunodeficiency disorder (Remold-O'Donnell et al. (1987) Blood 70(1):104-9; Remold-O'Donnel et al. (1984) J. Exp. Med. 159:1705-23).
Functional studies demonstrated that anti-CD43 monoclonal antibody stimulates the proliferation of peripheral blood T lymphocytes (Mentzer et al. (1987) J. Exp. Med. 1; 165 (5):1383-92; Park et al. (1991) Nature, 350:706-9) and the activation of monocytes (Nong et al. (1989) J. Exp. Med. 1:170(1):259-67). A monoclonal anti-CD43 antibody L11 blocks T cell binding to lymph node and Peyer's patch HEV. Antibody L11 inhibits T cell extravasation from the blood into organized secondary lymphoid tissues (McEvoy et al. (1997) J. Exp. Med. 185:1493-8). Monoclonal antibody recognizing CD43 molecule induces apoptosis of lineage marker-negative bone marrow hematopoietic progenitor cells (HPCs) that express CD34 at a high density (Bazil et al. (1996) Blood, 87(4):1272-81) and of human T-lymphoblastoid cells (Brown et al. (1996) J. Biol. Chem. 271:27686-95). Recent studies further indicated that CD43 functions as a ligand for E-selectin on human T cells (Matsumoto et al. (2005) J. Immunol. 175:8042-50; Fuhlbrigge et al. (2006) Blood, 107:1421-6).
Interestingly, scientists have also discovered that certain nonhematopoietic tumor cells, especially colorectal adenocarcinomas, do express CD43 molecules on the cell surface. Santamaria et al. (1996) Cancer Research, 56:3526-9: Baeckstrom et al. (1995) J. Biol. Chem. 270:13688-92; Baeckstrom et al. (1997) J. Biol. Chem. 272:11503-9; Sikut et al. (1997) , Biochem. Biophy. Res. Commun. 238:612-6. It has been shown that glycans on CD43 expressed in a colon carcinoma cell line (COLO 205) are different from those of leukocyte CD43 (Baeckstrom et al. (1997) J. Biol. Chem. 272:11503-9). Although it has been suggested that over-expression of CD43 causes activation of the tumor suppressor protein p53 (Kadaja et al. (2004) Oncogene 23:2523-30) and suppresses a subset of NF-kappaB target genes, partly via the inhibition of p65 transcriptional activity (Laos et al. (2006) Int. J. Oncol. 28:695-704), the direct evidence showing the causal role of CD43 in colon tumorigenesis is still lacking. The use of conventional anti-CD43 antibody as therapeutics for nonhematopoietic tumor cells is not practical due to its strong binding to both tumor and immune T cells. There remains a need to generate antibodies that specifically bind to a CD43 expressed on non-hematopoietic tumor or cancer cells, but do not bind to a CD43 expressed on leukocytes or other cells of hematopoietic origin. These antibodies may be useful as therapeutic agents for treating CD43 expressing nonhematopoietic cancer.
CEA is normally expressed in a variety of glandular epithelial tissues (such as the gastrointestinal, respiratory, and urogenital tracts) where it appears to be localized to the apical surface of the cells (Hammarstrom, S. (1999) Semin. Cancer Biol. 9, 67-81). In tumors arising from these tissues, there is an increasing level of CEA expression extending from the apical membrane domain to the entire cell surface, together with secretion of the protein into the blood (Hammarstrom, S. (1999) Semin. Cancer Biol. 9, 67-81). The excessive expression of CEA was observed in many types of cancers, including colorectal cancer, pancreatic cancer, lung cancer, gastric cancer, hepatocellular carcinoma, breast cancer, and thyroid cancer. Therefore, CEA has been used as a tumor marker and immunological assays to measure the elevated amount of CEA in the blood of cancer patients have long been utilized clinically in the prognosis and management of cancers (Gold P, et al. (1965) J. Expl. Med. 122:467-81; Chevinsky, A. H. (1991) Semin. Surg. Oncol. 7, 162-166; Shively, J. E. et al., (1985) Crit. Rev. Oncol. Hematol. 2, 355-399).
More importantly, CEA has become a potentially useful tumor-associated antigen for targeted therapy (Kuroki M, et al. (2002) Anticancer Res 22:4255-64). Two major strategies using CEA as a target for cancer immunotherapy have been developed. One method is the specific targeting of suicide genes (nitric oxide synthase (iNOS) gene) (Kuroki M. et al., (2000) Anticancer Res. 20(6A):4067-71) or isotopes (Wilkinson R. W. et al., (2001) PNAS USA 98, 10256-60, Goldenberg, D. M. (1991) Am. J. Gastroenterol., 86: 1392-1403, Olafsen T. et al., Protein Engineering, Design & Selection, 17, 21-27, 2004) to CEA-expressing tumor cells by anti-CEA antibodies. This method has also been extended to the use of antibody or antibody fragment conjugated with therapeutic agents, such as drugs, toxins, radionucleotides, immumodulators or cytokines. The other method is to utilize immunological cytolytic activities, specifically through antibody-dependent cellular cytotoxicity (ADCC) or complement-dependent cytotoxicity (CDC) to eliminate CEA-expressing tumor cells (Imakiire T et al., (2004) Int. J. Cancer: 108, 564-570). These methods often give rise to cytokine releases resulting in systemic side effects.
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